The compound represented by the formula (II') ##STR1## wherein R.sub.1 ' represents a hydrogen atom; an alkyl group; an alkoxy group; a cycloalkyl group; a cycloalkoxy group; an alkenyl group; an alkenyloxy group; a cyclohexenyloxy group; a phenyl group; a substituted phenyl group; a benzyl group; a substituted benzyl group; a trifluoromethyl group; or a halogen atom, [hereinafter referred to as the compound (II')] having an antiphlogistic and analgesic activity is disclosed in U.S. Pat. No. 4,126,625.
As a result of various studies, the present inventors have found that certain novel 2-substituted-carbamoylmethyl-3-methyl-5-substituted derivatives of benzo[b]furan prepared from the compound (II') have a strong muscle relaxant activity.